Exoplanets: Are We Close To Finding A New Earth? | Answers With Joe
发布时间 2017-07-10 12:30:00 来源
摘要
The search is on for Earth-like planets in our galaxy. Here's how we find them, what we've found so far, and what it means to us.
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LINKS LINKS LINKS:
Crash Course
https://www.youtube.com/watch?v=7ATtD8x7vV0
Open Education Edinburgh
https://www.youtube.com/watch?v=jvcgSMNjFGA
https://exoplanets.nasa.gov/interactable/11/
https://www.space.com/17738-exoplanets.html
http://www.planetary.org/explore/space-topics/exoplanets/transit-photometry.html
https://www.nasa.gov/kepler/discoveries
http://insider.si.edu/2013/05/new-method-of-finding-planets-scores-first-discovery/
https://www.cnet.com/news/farewell-hope-of-life-on-kepler-438b-it-was-good-while-it-lasted/
http://phl.upr.edu/projects/earth-similarity-index-esi
PARTIAL TRANSCRIPT:
Up until 1995, exoplanets were just a theoretical thing, but all that changed with the discovery of the first exoplanet, 51 Pegusi b. Or, 51 Peg for short.
It was what they came to call a “Hot Jupiter” because it was similar to Jupiter’s size and density, but it orbited extremely close to the star.
51 Peg B was found by a technique called Radial Velocity.
When a planet orbits its star, the planet’s gravity affects the star’s position just slightly. Same is true with the Earth and the moon.
So when viewed from above the planetary plane, it looks like the star has a tiny wobble. This is radial velocity.
But even if you’re viewing the system edge on, you can still measure radial velocity by measuring differences in the star’s wavelengths.
Thanks to the Doppler effect, when the star wobbles away from you, the light is slightly red-shifted. When it wobbles toward you, it’s slightly blue-shifted.
The rate and characteristics of the wobble can tell us a lot about the planet’s size and density, and perturbations in the wobble indicate the presence of multiple planets.
According to NASA, at the time of recording this, 639 planets have been found by radial velocity.
In 2009 the Kepler Space Telescope was launched with the specific purpose of measuring transits.
Transits occur when the orbital plane of a star just happens to line up edge on with our perspective and one of the planets passes in front of the star.
This dims the brightness of the star, very slightly, but by measuring the duration of the transit and the amount the light dims, you can learn a lot about the planet’s size, density, and distance from the star.
And through astro spectroscopy, we can tell whether the planet has an atmosphere and even the composition of elements in the atmosphere. And that can give us an idea of what the conditions on the planet are like.
The downside is that the vast majority of stars simply aren’t going to line up just perfectly for us to be able to view them this way.
Even still, the Kepler space telescope has confirmed the discovery of 2,335 exoplanets. 30 of which are rocky, less than twice the size of Earth, and in their star’s habitable zones.
And that’s just with Kepler. In all, 2732 exoplanets have been found using the transit method.
Other methods include Gravitational Microlensing.
A gravitational lens is a relativistic effect where the gravity of an object in the foreground bends the light of a distant star behind it.
We mostly use this with galaxy clusters, but it can also be used to discover planets. We’ve discovered 47 planets this way so far.
Another, called Astrometry, is similar to the radial velocity effect, but the wobble is in relation to other stars. So far only one planet has been found this way.
Direct imaging a planet is very difficult because the star is so bright that it’s hard to discern the planet from the star, especially at the distance we’re dealing with, but there are ways to put a proverbial thumb over the star so that we can detect the light bouncing off the planet.
Or the thermal signature of the heat the planet is absorbing from the star.
We’ve found 43 planets this way so far.
The diversity of planets we’ve found is mind-blowing. From the previously mentioned hot Jupiters to hot Neptunes, Puffy planets, which are like Jupiter but far less dense…
Planets like GJ-1214 B that are thought to be water worlds, totally covered by ocean…
To a planet we discovered in 2011 that’s thought to be made out of diamond.
Even rogue planets, floating throughout the galaxy without a star, probably flung out by all those hot Jupiters as they made their way through the solar system.
Some of the most Earth-like planets we've found include Kepler 438b, Kepler 442b, Gliese 667, and the TRAPPIST-1 system.
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